The present invention relates to an optical transmission element and, more particularly, to an optical transmission element having controlled stiffness characteristics for controlled bending behavior.
In practical experience, the requirements for transmission capacities of communications cables are steadily increasing. In order to achieve this the density of optical fibers in the cable cross section is increased. Groups of optical fibers are combined into so called fiber ribbons as optical fiber transmission elements for better handling and mechanical protection. These fiber ribbons can then advantageously be combined into so called ribbon stacks, which makes a very high density per cable cross section possible. Presently optical fiber ribbons with, for example, up to 24 optical fibers arranged in a common layer essentially parallel beside each other and embedded into a common firm plastic layer, are used in optical communications cables.
During ribbon manufacture it is often difficult to cover multiple optical fibers such as, for example, 24 optical fibers with a common plastic coating due to processing and quality reasons. During ribbon manufacture, manufacturing tools, for example, can cause vibrations and different fiber tensions which can result in dislocation and asymmetrical orientation of the optical fibers in the finished ribbon. Therefore, frequently optical fiber ribbons with smaller fiber count such as 4, 8 or 12 are manufactured and then combined with a common plastic layer into a ribbon having a higher fiber count. For the second coating with a common plastic layer normally the same UV cured material is used as for the coating for the individual combined optical fiber ribbons. By combining of sub-units of optical fiber ribbons one 12-fiber ribbon can be manufactured from three 4-fiber ribbons and a 24-fiber ribbon can be manufactured from three 8-fiber or two 12-fiber ribbons.
In order to be able to splice the optical fiber ribbons of ribbon units manufactured by combining individual fiber ribbons to each other, their ribbon material is stripped, i.e., the common plastic coating of the common second layer around the ribbon sub-units as well as the plastic coating of the individual fiber ribbons is removed along a given length. In practice this results in the problem that during stripping of the ribbon material, projections or irregular edges occur which are called xe2x80x9cwings.xe2x80x9d The apparent cause for this seems to be that the coating material for combining the individual ribbons does not combine sufficiently with the coating of the individual ribbons and, therefore, does not act like a singly manufactured plastic coating. This happens often in practice since commonly used ribbon materials often contain additives with separating compound characteristics so that there is no sufficiently stable bond between the coating material of the combination ribbon units and their own ribbon material. For stripping of the ribbon materials there are devices which simultaneously splice 8 or 12 fibers of the 8- or 12-fiber ribbon.
This invention is based on the objective of supplying an optical fiber transmission element whose common coating for combining the optical fiber sub-units combines trouble-free performance with the sub-units"" plastic coatings. This goal is achieved by an optical fiber transmission element mentioned in the beginning where a binding agent is applied to the first coating around the respective sub-units which causes adhesion of the plastic matrix of the second common coating to the respective plastic matrix of the first coating of the two optical fiber sub-units.
The binding agent on the plastic coatings of the respective optical fiber sub-units achieves an improved bonding of their plastic materials to the plastic matrix of the common outer coating for combining the optical fiber sub-units so that these two coating layers essentially function as a unit, i.e., a single plastic coating around the optical fiber. In this way during stripping of the plastic coating, so called xe2x80x9cwingsxe2x80x9d, i.e., projections or irregular edges are avoided and precise sharp edges for the optical fiber sub-units are made possible.
The invention further concerns the process for manufacturing a fiber optic transmission element with at least a first and at least a second optical fiber sub-unit where multiple optical fibers are inserted into a first plastic coating for formation of the respective optical fiber sub-units and where these two optical fiber sub-units are combined by a common second coating which is characterized by the fact that at least one binding agent is applied to the plastic coating of the respective optical fiber sub-unit which causes the bonding of the plastic matrix of the common second coating to the respective plastic matrix of the first coating of the two optical fiber sub-units.
The invention also concerns a device for manufacturing an optical transmission element with at least a first and at least a second optical fiber sub-unit where one coating device respectively is provided which can insert multiple optical fibers into a first plastic coating and where a further coating device is provided which can combine the two optical fiber sub-units by a common second plastic coating, which is characterized by the fact that additional coating means are provided which can add at least one binding agent to the first plastic coating of the respective optical fiber sub-unit which effects a bonding of the plastic matrix of the common second coating to the respective plastic matrix of the first coating of the at least two optical fiber sub-units.